The X-ray crystal and molecular structure of 5′-bromo-5′-deoxythymidine

5′-Bromo-5′-deoxythymidine (1) crystallizes with four molecules in a monoclinic unit cell of space group C2. The ribose ring adopts an envelope conformation, transient between T and E₀ (O4′-exo), with the C1′ atom being in the flap position. In the crystal lattice, the molecules are connected by intermolecular one-dimensional chains of hydrogen bondings from the hydroxyl hydrogen H3′(O3′) to the carbonyl oxygen O4. The differences in conformation and a hydrogen-bonding system of 1 with comparison to the structure of thymidine are observed. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 591–596, 1998     

Erstes Beispiel einer H-Verschiebung in ‘Thiocarbonyl-aminiden’ (N-(Alkylidensulfonio)aminiden)

First Example of an H-Shift in ‘Thiocarbonyl Aminides’ (N-(Alkylidenesulfonio)aminides) Reaction of benzyl azide ( 15a ) with the sterically hindered C?S group of 4,4-dimethyl-1,3-thiazole-5(4H)-thiones 14 (Scheme 3) and 1,1,3,3-tetramethylindane-2-thione ( 17 , Scheme 4) at 80° leads to the corresponding imines in high yield, without formation of any by-product. In contrast, 15a and 2,2,4,4-tetramethyl-3-thioxocyclobutanone ( 7 ) under the same conditions yielded, in addition to imine 19 , products 20a and 21 (Scheme 5). For the formation of 20a , a reaction mechanism via [1,4]-H shift in the intermediate ‘thiocarbonyl aminides’ 23 is proposed (Scheme 6). Product 21 as well as the dithiazole derivative 22 , which is formed only in the reaction with 4-nitrobenzyl azide ( 15c ), are formal adducts of the dipole 23 . Whereas precedents are known for the formation of cycloadducts of type 22 , the pathway to 21 is not known. Two possible mechanisms of its formation are proposed in Schemes 8 and 9.     

The comparison of geometric and electronic properties of molecular surfaces by neural networks: Application to the analysis of corticosteroid-binding globulin activity of steroids

Summary It is shown how a self-organizing neural network such as the one introduced by Kohonen can be used to analyze features of molecular surfaces, such as shape and the molecular electrostatic potential. On the one hand, two-dimensional maps of molecular surface properties can be generated and used for the comparison of a set of molecules. On the other hand, the surface geometry of one molecule can be stored in a network and this network can be used as a template for the analysis of the shape of various other molecules. The application of these techniques to a series of steroids exhibiting a range of binding activities to the corticosteroid-binding globulin receptor allows one to pinpoint the essential features necessary for biological activity.     

Capillary electrophoresis study of systemin peptides spreading in tomato plant

Systemin (Sys) is an 18‐aa plant peptide hormone involved in the regulation of plant's defensive response. Sys is considered as a fast‐spreading systemic wound signal. We developed a simple and rapid CE method to monitor the spreading of Sys peptides through tomato plant. A 1,2,3‐triazole‐linked AZT‐systemin conjugate was designed as a model to study the possibility of translocating small cargo molecules 3'‐Azido‐2',3'‐dideoxythymidine by systemin. The Sys peptides (Sys, N‐propiolyl Sys, and AZT‐systemin conjugate) were injected into the stem and leaves of mature tomato plant. Its transportation throughout the plant tissue was traced by CE. The peptides were clearly visible in the crude tomato exudates and an optimum separation was achieved in 25 mM phosphate “buffer” at pH 2.5 and a voltage of 20 kV using uncoated fused silica capillary. CE analysis showed that Sys peptides are well separated from tomato plant exudates ingredients and are stable in tomato stem and leaf exudates for up to 24 h. CE study revealed that the Sys peptides are effectively spreading throughout tomato stem and leaves and the peptides could be directly detected in the crude plant matrixes. The translocation was strongly inhibited by sodium azide. The results showed that the established CE method can be used to characterize plant peptides spreading under plant physiological conditions.     

Mechanism of Catalyst Action in Interfacial Polycondensation of Chlorobisphenol and Isophthaloyl Chloride

The mechanism of action of quaternary ammonium salt catalysts in the synthesis of aromatic polyesters was investigated. The possibility of formation of compounds of these salts and bisphenols and their extraction in the form of an ion pair into the organic phase was investigated. The structure of the compounds obtained was determined.     

Impact of Heteroatom Substitution on Dual-State Emissive Rigidified 2-(2’-hydroxyphenyl)benzazole Dyes: Towards Ultra-Bright ESIPT Fluorophores**

2-(2’-Hydroxyphenyl)benzazole (HBX) fluorophores are well-known excited-state intramolecular proton transfer (ESIPT) emitters largely studied for their synthetic versatility, photostability, strong solid-state fluorescence and ability to engineer dual emission, thus paving the way to applications as white emitters, ratiometric sensors, and cryptographic dyes. However, they are heavily quenched in solution, due to efficient non-radiative pathways taking place as a consequence of the proton transfer in the excited-state. In this contribution, the nature of the heteroring constitutive of these rigidified HBX dyes was modified and we demonstrate that this simple structural modification triggers major optical changes in terms of emission color, dual emission engineering, and importantly, fluorescent quantum yield. Investigation of the photophysical properties in solution and in the solid state of a series of ethynyl-TIPS extended HBX fluorophores, along with ab initio calculations demonstrate the very promising abilities of these dyes to act as bright dual-state emitters, in both solution (even in protic environments) and solid state.